美国俄亥俄州立大学Shiyu Zhang团队报道了Tricopper团簇上的多重质子耦合电子转移。相关研究成果于2022年1月19日发表在《美国化学会杂志》。

酶中的金属簇通过在狭窄的电位范围内积累多个氧化还原当量来进行维持持续的反应。这种在自然界中普遍观察到的氧化还原电位平衡效应尚未在合成金属簇中重现。

该文中，研究人员采用一种完全封装的合成三铜配合物来模拟多铜氧化酶（MCOs）中天然中间体CuiCuiI（μ3-O）（NI）完全还原的三核铜簇CuiCui（μ2-OH2）（FR）的三电子双质子还原再生。tricopper团簇可以获得四种氧化态（I，I，I至II，II，II）和四种质子化态（[Cu3（μ3-O）]LH、[Cu3（μ3-OH）]L、[Cu3（μ3-OH）]LH和[Cu3（μ3-OH2）]L，其中LH表示质子化配体），从而能够对与MCOs相关的质子耦合电子转移（PCET）进行机理研究。七种具有离散氧化和质子化状态的tricopper配合物通过光谱或X射线单晶衍射进行了表征。

建立了CuiCuI（μ3-O）LH还原为CuiCuI（μ3-OH）L的逐级电子转移-质子转移（ET-PT）机制，确定了将CuICuICuI（μ3-OH）LH还原为CuICuICuI（μ2-OH2）L的逐步PT–ET机制。从ET–PT转换为PT–ET机制表明，tricopper络合物可以采用不同的PCET机制来绕过高势垒质子转移步骤。总的来说，三电子双质子还原发生在170 mV的窄电位范围内，体现了次级质子继电器在金属簇上传递多个氧化还原当量时的氧化还原电位均衡效应。

附：英文原文

Title: Multiple Proton-Coupled Electron Transfers at a Tricopper Cluster: Modeling the Reductive Regeneration Process in Multicopper Oxidases

Author: Weiyao Zhang, Curtis E. Moore, Shiyu Zhang

Issue&Volume: January 19, 2022

Abstract: Metal clusters in enzymes carry out the life-sustaining reactions by accumulating multiple redox equivalents in a narrow potential range. This redox potential leveling effect commonly observed in Nature has yet to be reproduced with synthetic metal clusters. Herein, we employ a fully encapsulated synthetic tricopper complex to model the three-electron two-proton reductive regeneration of fully reduced trinuclear copper cluster CuICuICuI(μ2-OH2) (FR) from native intermediate CuIICuIICuII(μ3-O) (NI) in multicopper oxidases (MCOs). The tricopper cluster can access four oxidation states (I,I,I to II,II,II) and four protonation states ([Cu3(μ3-O)]LH, [Cu3(μ3-OH)]L, [Cu3(μ3-OH)]LH, and [Cu3(μ3-OH2)]L, where LH denotes the protonated ligand), allowing mechanistic investigation of proton-coupled electron transfer (PCET) relevant to MCOs. Seven tricopper complexes with discrete oxidation and protonation states were characterized with spectroscopy or X-ray single-crystal diffraction. A stepwise electron transfer–proton transfer (ET–PT) mechanism is established for the reduction of CuIICuIICuII(μ3-O)LH to CuIICuIICuI(μ3-OH)L, while a stepwise PT–ET mechanism is determined for the reduction of CuIICuICuI(μ3-OH)LH to CuICuICuI(μ2-OH2)L. The switch-over from ET–PT to PT–ET mechanism showcases that the tricopper complex can adopt different PCET mechanisms to circumvent high-barrier proton transfer steps. Overall, three-electron two-proton reduction occurs within a narrow potential range of 170 mV, exemplifying the redox potential leveling effect of secondary proton relays in delivering multiple redox equivalents at metal clusters.

DOI: 10.1021/jacs.1c10948

Source: https://pubs.acs.org/doi/10.1021/jacs.1c10948